Description

METHOD FOR THE CREATION OF A FOUNDATION PILE

The subject of this invention is a method for the creation of a foundation pile.

Foundation pilings are normally used to increase the load-bearing capacity of building foundations, whether they are buildings, bridges, etc. ... In fact, where the ground is sinking, it may be necessary to offload the weight of buildings onto deeper layers of soil that are able to guarantee a suitable compressive strength. This is currently done by installing a number of vertical piles beneath the foundations of the buildings; the bottoms of these piles rest on deeper layers of ground, while the tops are connected to the foundations. Foundation pilings may be created before a building is erected or later (for example, following collapses occurring in the interim).

Currently, in accordance with an initial form, foundation piles are created by making a hole in the ground, inserting a tubular casing and then filling it with a cement-based cast. According to a second known form, the foundation piles are pre-fabricated rigid elements - in many cases, modular - that are inserted into the soil at the foundations, either by being driven in directly or through the prior creation of a vertical hole.

In all cases, when the piling needs to be created at the foundations of existing buildings, the insertion/creation of piles in the ground occurs through holes that are also made through the foundations themselves.

Various examples of foundation piles are described, for example, in the patents WO 2005/028759, GB 2150612, US 975488, US 1366179, US 5713701, EP 0413422, GB 2179083, GB 2299360, GB 2351516, GB 521683, US 5228807, US 5288175, GB 1213548, US 5228806, GB 2261456, US 3820347, GB

2330370, EP 0758699, DE194125, GB 1592591, JP 8246448 and EP 0056287. Known technology does, however, present several problems. In the first place, piles created using known technology are relatively complicated and expensive to make. Secondly, in the case of existing buildings, piles as known require relatively large holes to be made in the foundations of the building (holes with dimensions substantially corresponding to that of the pile section).

Moreover and still in the case of existing buildings, securing the pile to the foundations is also a particularly complex process. It should be noted that these piles will be stressed by the foundations, mainly in terms of compression.

Nonetheless, the foundations have through holes level with the piles that therefore require plugging with a great deal of care.

It should also be noted that when holes are made previously in the soil, on one hand there is a problem of having to dispose of the soil removed and on the other, of the creation of underwashing in the surrounding soil which can undermine the hold of the foundations in adjacent buildings.

It should be remembered that there are also other methods of soil consolidation, where expanding resins are injected beneath the building (see, for example, patent EP 851 064 under the name of Uretek). According to these consolidation methods, vertical holes are created under the foundations of the buildings and it is through these that the resin is injected into the soil. The resin then expands and should be able to compact and consolidate the soil.

These methods of consolidation too are not without their problems. In fact, due to the non-homogenous composition of the soil and to the pressure of the foundations on same, the resins tend to expand in the directions where they meet the least resistance; therefore, they often tend to move away from the area concerned, leading to excessive resin consumption, which is costly and also useless. As a result, consolidation operations performed in this way may, in the long term, turn out to be unable to guarantee the correct amount of support to the

building. This problem is particularly present in the case of clay soils. hi this situation, the technical task at the basis of this invention is to devise a method for the creation of a foundation pile to overcome the problems mentioned above. In particular, it is the technical task of this invention to devise a method for the creation of a foundation pile that is simple and relatively economical to complete.

It is also the technical task of this invention to devise a method for the creation of a foundation pile that can be easily secured to the foundations of existing buildings and reduces damage to said foundations to a minimum.

The specified technical task and the aims indicated are substantially achieved by a method for the realisation of a foundation pile according to that described in the attached claims.

Further characteristics and the benefits of this invention will become more evident from the detailed description of some of the preferred but not exclusive embodiments of a method for the creation of a foundation pile as illustrated in the annexed drawings, in which:

- Figure 1 shows a schematic side view of a first embodiment of a first stage of the method that is the subject of this invention; - Figure 2 shows a schematic side view of a second stage of the method that is the subject of this invention;

- Figure 3 shows a schematic side view of a third stage of the method that is the subject of this invention;

- Figure 4 shows a schematic side view of a fourth stage of the method that is the subject of this invention;

- Figure 5 shows a schematic side view, enlarged compared to the previous figures, of a fifth stage of the method that is the subject of this invention;

- Figure 6 shows a schematic side view of a sixth stage of the method that is the subject of this invention; - Figure 7 shows a schematic side view of a possible alternative to the

method that is the subject of this invention; and

- Figure 8 shows a schematic side view of a further possible alternative to the method that is the subject of this invention.

All of the annexed figures illustrate a case where the foundation pile 1 is created below existing foundations 2. In all of the annexed figures therefore, it is possible to see a vertical section of the soil 3 and of the foundations 2, corresponding to the area where the foundation pile 1 is realised.

According to this invention, the first necessary stage for the creation of a foundation pile 1 includes the creation, in the soil 3, of a hole 4 with a generally vertical development axis and its own pre-determined cross section.

According to requirements, there are different ways in which the hole 4 can be created.

According to a first embodiment, the hole 4 can be made by boring with a drill 5 (solution illustrated in Figure 1) with or without removal of the material. In this case, the depth of the hole 4 needs to be established beforehand using known methods.

In other embodiments (not illustrated), on the other hand, the execution of the hole 4 in the soil 3 may occur by driving without removing any material. In this case it may be advantageously decided to use a boring head with a section corresponding to the hole 4 to be made. This is planted into the soil 3 by percussion or thrust on a shaft connected to the head. Shafts with a section less than that of the bit are preferably used (to prevent lateral friction) which, in the event that there is little available space, can be comprised of modular jointed elements. According to this operating mode, the depth of the hole 4 is decided while work is ongoing, given that the head driving proceeds until the resistance of the soil 3 reaches a pre-set limit which is considered to be sufficient (normally a depth of several metres). At this point, the shaft is separated from the head and retracted from the hole 4.

As already mentioned, the creation of the foundation pile 1 can occur either before a building is commenced or at a later stage (while building work is ongoing

or after the building has been completed).

In the first case, the hole 4 is made directly in the soil 3, starting from the foundation bed.

In the second case, however, the hole 4 is also made through the foundations 2 of the building (case illustrated in the annexed figures).

Once the hole 4 is completed, this invention foresees a stage of compacting

^■ the soil 3 around the hole 4, which occurs by widening the cross section of the hole 4 itself (Figures 2 to 4). The purpose of this stage is, on one hand, to create a side wall for the hole 4, which is both compact and substantially free of communication passages with the interstices in the soil 3 around it, and on the other hand, of increasing the load-bearing capacity of the soil around the hole itself. Of course, the increased capacity will depend on the extent of the widening action on the hole as well as on the type of soil concerned.

Specifically, according to the preferred embodiment of this invention, the compaction stage takes place without removing material and foresees the compression of the soil 3 in outgoing radial directions compared to the development axis of the hole 4.

The embodiment illustrated in the annexed figures shows that this is achieved by inserting into the hole 4 at least one fluid dilator 6 (pneumatic or hydraulic), which is made to expand radially by supplying it with a pressurised working fluid (such as air, water, oil, etc.).

The fluid dilator 6 can advantageously be comprised of a dilating pipe 7

(made in rubber, etc., for example and reinforced, if necessary, with metal inserts) closed at the top end by a fitting 8 to supply the working fluid, and at the bottom by a closing element 9. Moreover, it can be foreseen for the dilator 6 to be made in such a way that, as it dilates, it may be subject to a certain shortening.

When the pressurised working fluid is supplied to the dilator 6 by a special pump or compressor 10, its dilation causes radial compression in the soil 3 around the hole 4, as well as a resulting enlargement of the hole until it reaches the maximum dimensions that can be reached by the dilator 6. Note that already at

pressures within a range of 15/20 kg/cm2, it is possible to arrive at good compression levels in the soil 3.

If the length of the hole 4 exceeds that of the dilator 6, compaction may be planned for several successive stages, gradually moving the dilator 6 along the development axis of the hole 4, as illustrated as an example in the annexed figures, where compaction takes place in two successive stages (positions in

Figures 2 and 4).

Moreover, it may be foreseen for compaction to take place in several successive stages where a succession of dilators with increasing maximum dimensions is used for each portion of the hole 4 (given a certain initial dimension of the hole 4, it is in fact difficult to make dilatators able to increase the section sufficiently with a single dilation).

For example, a single preferred embodiment, includes the making of an initial hole 4 with a diameter of 30 mm, and a subsequent dilation stage up to 55 mm, using a first dilator 6 with a section a little under 30 mm. A further widening is foreseen (with resulting compaction) using a dilator 6 with a section just under

55 mm, able to take the section of the hole 4 up to 95 mm.

As can be seen, therefore, each dilator 6 is generally able to increase the section of the hole 4 by a little under twice as much. It should also be noted that the widening stage does not concern any part of the hole 4 made through the foundations 2, but only the part created directly in the soil 3.

Once the compaction of the soil 3 around the hole 4 has been completed (the extent of the compaction is established from time to time, also taking into account the type of soil 3 concerned by the intervention), there is a strip of compacted soil 11 around the hole, indicated by denser shading in the annexed figures.

The method that is the subject of this invention includes a stage of pouring at least one solidifiable filler inside the hole 4, leaving said filler to cure until the column structure defining the foundation pile 1 is obtained. According to requirements, the filler may be liquid or semi liquid.

According to a first embodiment, the filler is formed by a cement-based compound (with the addition of bentonite, if necessary).

According to a second embodiment, the filler is comprised of a resin, expanding or otherwise. In the preferred embodiment, however, the filler is comprised of an expanding resin 12, given that, in view of its expansion, this product is able to adhere to the soil 3 in the best possible manner. Hereinafter, reference will be made exclusively to expanding resins 12, but the same considerations (with the necessary arrangements to suit the case) must be considered valid for any other type of filler.

It should be noted that, thanks to the previous compaction operation, where the side walls of the hole 4 were compacted, the volume into which the resin 12 expands is that of the hole 4 only. Infiltration of the resin 12 into the surrounding soil 3 is prevented. For the best possible resin (or other filler) injection, before the casting stage, it is preferable for there to be another stage in which a plug 13 is created level with the top end of the hole 4, as well as a stage for positioning at least one injection pipe 14 (advantageously disposable) through this plug 13. According to the applications and the depth of the hole, it is possible to use several injection pipes 14 of different lengths.

In the embodiment illustrated (Figure 5) the plug 13 has been made level with the section of the hole 4 obtained through the foundations 2, for example, cementing the injection pipe 14 in this section of the hole 4.

According to requirements, the positioning stage for the injection pipe 14 can be carried out so as to place the bottom end of the injection pipe 14 at a predefined depth inside the hole 4. As a result, while in the annexed figures, the bottom end of the injection pipe 14 is positioned level with the plug 13, in other embodiments, it may be positioned halfway down the hole 4, in proximity to the bottom section of same, etc.... When more than one pipe is used, the bottom end of each is positioned at a different depth.

Once the injection pipe 14 has been positioned, it is connected to a supply unit 15 for the resins 12, which then proceeds to fill the hole 4.

Preferably, it should be foreseen that the casting stage is carried out using high-density expanding resins 12 (advantageously between 300 and 500 kg/m3), with an expansion coefficient of less than four (preferably between two and three times) and with curing times (solidification) of between 40 and 80 seconds. In fact, in this way, it is possible to create piles with a high degree of compressive strength (even in the range of 150-200 kg/cm2). hi any case, according to the applications, it may even be foreseen that before the casting stage, there is a stage when reinforcement material for the foundation pile 1 is inserted into the hole 4. hi particular, as illustrated in the

Figures 7 and 8, this insertion stage may include the insertion into the hole 4 of a reinforcement support 16 and/or aggregates 17 (such as washed, fine gravel). In turn, the reinforcement support 16 may be formed by a complex structure as in Figure 7, or by simple bars, tubes or round elements; it can be made in metal or manmade fibres.

As a result, when the work is completed, the reinforcement support 16 is sunken into a matrix formed by the hardened resin 12 (or other solidified fillers) used to define the column structure of the pile. It should also be noted that, when aggregates 17 are used, it is particularly advantageous to position the bottom end of the injection pipe 14 level with an intermediate section of the development of the hole 4, or to use several injection pipes 14, to make resin 12 penetration into the interstices formed by the aggregates 17 as even as possible. This invention presents significant advantages.

In the first place, the method that is the subject of this invention means it is possible to realise foundation piles simply, quickly, with little effort and at relatively little cost. hi the second place, even in the case of piles created beneath existing foundations, thanks to the fact that the hole made in the foundations has a notably

smaller section than that of the pile, on one hand, damage to the foundations is reduced to a minimum while on the other, the connection of the pile to the foundations is not necessary, given that the undamaged parts of the latter can rest directly on the top surface of the pile. As already mentioned, thanks to the compression stage for the soil around the hole 4, it is possible to prevent the filler from seeping into it. As a result, the ^• amount of filler used to fill the hole is always found to be optimum when the work is completed.

Moreover, thanks to the method used in this invention, as well as the support guaranteed by the piles, there is also the benefit of greater support from the compacted soil around the piles themselves.

Last but by no means least, thanks to the method that is the subject of this invention, the use of drills is avoided or in any case, reduced to a minimum, with the resulting advantage in terms of the risk of creating underwashing, as well as in terms of the masses of earth to be removed.

It should also be considered that this invention is relatively easy to realise and that the costs connected to its implementation are not very high.

The invention thus conceived is open to numerous changes and variations, all of which fall within the inventive concept that characterises it. All details can be replaced by other technically equivalent elements and in practice, all of the materials used, as well as the forms and dimensions of the different parts can be of any kind, as per requirements.